The present invention relates to palletized modular work stations used with asynchronous conveyor systems.
Palletized conveyors transporting pallets between work stations along xe2x80x9ctransfer linesxe2x80x9d, with each pallet holding work pieces in a precise location using fixtures rigidly mounted to the pallets, have been available for many years. The pallets are conveyed along a conveyor line, lifted off of the moving conveyor, rigidly clamped for a work operation, and then released and returned to the moving conveyor to allow subsequent work operations to be performed down-line. Removal of the pallet off of the conveyor provides two advantages: it allows the conveyor to continue moving without having to stop for a work operation, and it also isolates the pallet from conveyor vibrations during work operations. Examples of such systems are disclosed in U.S. Pat. No. 4,570,782 to Cargill; U.S. Pat. No. 4,629,384 to Beshke; U.S. Pat. No. 4,639,963 to Fisher; and U.S. Pat. No. 5,860,505 to Metzger.
There are disadvantages associated with known palletizing conveyor systems. For example, some systems require the use of customized pallets having ground surfaces to facilitate pallet clamping and registration after the pallet has been removed from the conveyor chain or drive media. These systems are expensive, and consist of heavy-duty castings designed to support pallets as heavy as one ton or more. Replacing tooling on such systems is similarly expensive. The wedge-lock principle of registration they employ also requires the engagement of a significant pallet surface area, which can result in mis-registration due to the trapping of foreign particulate on the surface contact areas.
Accordingly, it is an object of the present invention to provide an asynchronous palletized conveyor system which is a lighter-duty version than known heavy-duty systems, and which is manufactured in a substantially more economical manner.
Another object of the invention is to provide such a system which is xe2x80x9cmodularxe2x80x9d in the sense that it provides a fixture-carrying device that is standardized and may be used with a variety of work pieces, to perform a variety of work functions on the work pieces, using relatively inexpensive tooling and pallets/pallet carriers.
Still another object is to provide such a system which employs locating mechanisms that rigidify the pallet in precise location within three (X, Y and Z) dimensions, and which do not require changing fixture designs commonly in use for accurately locating a workpiece on a pallet in three dimensions.
A further object is to provide a reliable mechanical clamping lock for the pallet when the pallet has been disengaged from the conveyor chain or drive media and has been brought into a registration position.
Yet another object is to provide such a system which provides a shielding mechanism against trapped foreign particulate which may interfere with the pallet locating mechanism and cause mis-registration of the pallet.
The following terms are used in the claims of the patent as filed and are intended to have their broadest meaning consistent with the requirements of law. Where alternative meanings are possible, the broadest meaning is intended. All words used in the claims are intended to be used in the normal, customary usage of grammar and the English language.
xe2x80x9cAsynchronousxe2x80x9d palletized conveyor system means a system in which operations are performed at varying times on different palletized work pieces at work stations located along a particular conveyor, so that each pallet may be lifted from a conveyor chain or drive media and returned to a moving conveyor without the need to halt the conveyor.
xe2x80x9cConveyorxe2x80x9d means any mechanism or means for transporting pallets between work stations, whether in a closed circuit or open circuit fashion, and whether using belts, chains, power rollers or other mechanisms or means.
xe2x80x9cForeign particulatexe2x80x9d means foreign particles, such as metal shavings, either generated by work operations performed on the fixture or deposited by other means.
xe2x80x9cRegistrationxe2x80x9d or xe2x80x9cestablishes registrationxe2x80x9d means that a pallet is brought into engagement with one or more location blocks, so that the pallet is fixed in position and accurately located with respect to three (X, Y, Z) dimensions.
xe2x80x9cRegistration engagement mechanismsxe2x80x9d mean devices used to locate and connect the pallet to the location block of the work station, such as but not limited to the engagement pins and tooling pads.
xe2x80x9cThree dimensionsxe2x80x9d or xe2x80x9cX, Y and Z dimensionsxe2x80x9d means the two horizontal dimensions, length and width (X, Y) and the vertical dimension, height (Z).
The objects mentioned above, as well as other objects, are solved by the present invention, which overcomes disadvantages of prior art asynchronous palletized conveyor systems and mechanism, while providing new advantages not believed associated with such systems and mechanisms.
The present invention is directed to an asynchronous system for conveying a pallet between one or more work stations and facilitating work operations upon a fixture located on the pallet. In another embodiment, the invention consists of the work station itself. Both the system and the work station are now described.
A preferred embodiment of a system according to the present invention includes a conveyor for continuously moving the pallet between the one or more work stations located along the conveyor system. Each of the one or more work stations includes opposed location blocks located adjacent to the conveyor. The location blocks are provided with a first set of registration engagement mechanisms. The pallet is provided with a second set of registration engagement mechanisms. A lifting and locking mechanism is employed to remove the pallet from the conveyor chain or drive media and for locking the pallet into a rigid registration position at which the pallet is brought into accurate registration, along X, Y and Z dimensions, with the opposed location blocks through connection of the first and second sets of registration engagement mechanisms.
In a particularly preferred embodiment, the first set of registration engagement mechanisms includes a plurality of locating bushings and locating pads, while the second set of registration engagement mechanisms includes a plurality of engagement pins and tooling pads. Connection of the locating bushings and engagement pins establishes registration of the pallet with respect to the opposed location blocks along the X and Y dimensions, while connection of the locating pads and tooling pads establishes registration of the pallet with respect to the opposed location blocks along the Z dimension.
In a preferred embodiment, the lifting and locking mechanism includes a pressurized cylinder, which may be a pneumatic cylinder, driving two pairs of pivotally attached links. Each of the links may be pivotally connected to a link arm terminating in a wedge. Vertical movement of the cylinder may cause link arms to exert a lateral force on the wedges, which in turn may exert a lifting force on the pallet sufficient to lift the pallet off of the conveyor and lock the pallet into a fixed position above the conveyor and into the engaged registration position. Angled surfaces on the sides of the pallet mirroring angled surfaces on the wedges may be provided to facilitate engagement of the wedges with the pallet, and to transmit lateral wedge movement into vertical pallet movement. In a particularly preferred embodiment, the angled engaging surfaces on the wedges form an angle of about 20xc2x0 with a horizontal plane. Preferably, the pallet has opposed, substantially planar side surfaces.
In another preferred embodiment, and to provide additional flexibility to the use of the present invention, a pallet carrier may be used to mount the pallet, and may be carried by the conveyor.
In another preferred embodiment, the locating pads in the location blocks are in fluid communication with air passages supplied with pressurized air, so that foreign particulates may be removed from the pad area prior to pallet registration with the fixed location blocks. One or more pressure switches may also be provided to monitor the flow of pressurized air within the air passages. In one preferred embodiment, if a predetermined minimum air flow is detected after registration of the pallet with the opposed location blocks, an alarm is provided to alert the user to the fact that mis-registration may have occurred, perhaps due to the presence of foreign particles such as metal shavings in a registration area. Alternatively, the locating bushings may be provided with air passages supplied with the pressurized air, for the same purpose. In yet another alternative embodiment, other mechanisms, such as wipers, may be provided for shielding, obstructing or removing foreign particulate from registration areas such as areas in or adjacent to the engagement pins or tooling pads.